SACEA COAL JIGGING IN SOUTH AFRICA

Transcription

1 29 July 2010 SACEA COAL JIGGING IN SOUTH AFRICA Mauritz Lundt

2 Content 1 Background of Jiggingi Why Jigging coal and Benefits of Jigging? Principles of Jigging operations Conclusions

3 Background 2 History of coal Jigging in South Africa Natal First record of coal washing in Natal goes back to 1905 Between 1905 and 1910 five jig jgplants were installed to produce coking coal The plants processed about tons out of the total production of (8%) Raw coal mined in those days had a calorific value of 14 lbs/lb (31.6 MJ/kg) Virtually all coal below 6 mm was discarded (about 20% of production) Situation changed little until 1926 where after there was a steady increase in tonnage of coal washed

4 Background 3 History of coal Jigging in South Africa Transvaal and Orange Free state Large jig plant (Basch type jigs) installed in 1909 but de-commissioned after 8 years No coal washed until 1934 In 1934 a Rheolaveur plant was built in the Witbank area to produce a blend coking coal In 1935 the first Chance sand plant was commissioned at Vereeniging Total of 18 plants by 1956 Approximately 60 coal preparation plants in SA today

5 Why Jigging coal and Benefits 4 Smaller footprint t Lower capital costs Lower operating costs Simple process not a complicated flow and equipment

6 Jigging at Leeuwpan 5 Tip bin Primary crusher 100t feed silo Dabmar screens Jig De-grit cyclones De-watering screens Secondary crusher Product crusher Discard bin Bucket Elevator 40kt product stockpile

7 Simplified flow sheet for a Jig plant 6 JIG PLANT DMS PLANT

8 Principles of Jigging operations 7

9 Principles of Jigging operations 8 Parameters to address in the Jig plant Pre Jig Plant feed tempo Fines tempo/size distribution Feed distribution Jig Jig feed tempo Bed Depth Operating pressure Strokes/Minute Air-Water Interface Float settings Hatch water in Jig Feed size distribution After Jig Raw water levels Water on Product screen Induction cyclones Thickener feed Thickener Underflow WHAT MAKES JIGGING COMPLICATED WHAT MAKES JIGGING COMPLICATED IS THAT THERE IS A LOT OF INTERDEPENDANCY BETWEEN THESE VARIABLES.

10 Principles of Jigging operations 9 Pre-Jig Plant feed tempo Control the feed to the jig to 100t/h per meter width (Applicable for Course coal Jigging) Fines tempo/size distribution The narrower the feed size distribution the more efficient the Jig will operate The ratio between the top size and bottom size should be 3:1 Feed distribution The feed to the Jig must be evenly spread through the whole width of the Jig

11 Jig Feed tempo/distribution 10

12 Feed Distribution 11 Segregation g of coarse and fine material in the feed an uneven distribution of material in the jig. Negative effect on stratification of the material in the jig jg

13 Principles of Jigging operations 12 JIG Jig feed tempo Must be controlled not to overload the Jig Bed Depth Must be controlled with the weir bars in order to obtain maximum separation Operating pressure Must be optimized to obtain maximum stratification Strokes/Minute Must be optimized to obtain maximum stratification

14 Principles of Jigging operations 13 JIG Air-Water Interface Must be measured and controlled to have the most efficient Jigging action Float settings Must be set according to the washability of the feed Hatch water in Jig Must be sufficient to obtain maximum stratification

15 Bed Depth 14

16 Bed Depth 15 Bed Depth Weir Bars Bed depth for course coal varies mm thick Thick bed depth increased particle residence time, improved stratification and less misplacement to product and discard

17 Operating Pressure 16 Operating Pressure With a thicker coal bed, the operating air at least 0.36 bar. Higher operating pressure resulted in an increase in the pulse amplitude, lift and open the bed

18 Pulse Settings - Strokes/Minute 17 Air valve timings i

19 Pulse Settings - Strokes/Minute 18

20 Pulse Settings - Strokes/Minute 19 Pulse Settings The pulse settings are probably some of the most important variables Four time periods (T) periods. Pulse time (T1), Hold time (T2), Exhaust time (T3) and Delay time (T4) T1 T2 T3 T4 Water pulse cycle Product pulse cycle Cycle timing

21 Air water interface 20 Measuring of the Air-water interface Obtain a constant stroke/pulse during operation

22 Automated pulse system - Leeuwpan s Installation 21 20mA 300mm 850mm 900mm 0mA Offset 250mm

23 Automated pulse system - Leeuwpan s Installation 22 STROKE 600mm Outlet shorter 550mm Working Range Outlet 500mm Outlet longer Inlet longer / working air less 250mm Working Range Inlet 200mm Inlet shorter / working air less When the water level does not reach the outlet working range limits the timing of the outlet poppet valves is adjusted When the water level does not reach the inlet working range limits the timing of the inlet poppet valves is adjusted Stroke = actual upper reading - actual lower reading 0mm

24 Automated pulse system - Leeuwpan s Installation 23 PLC showing the leveling li probe readings and set points

25 Leeuwpan s PLC 24 PLC showing the poppet valve readings and set points

26 Float Settings 25 A float is a device that t floats within the Jig bed to indicate the height ht of the discard bed The float is heavy enough to lie within the coal layer but on top of the discard layer A pre-set high and low discard bed level can be set on the PLC, which controls the opening and closing of the gates The floats settings can be changed by: Adding weights on top of the float Changing the PLC setting

27 Improvement process - Float Settings 26 Float PRODUCT Set point height Gate DISCARD

28 Float Settings 27 Float gewigies SG 1.2 SG 1.4 SG 1.6 SG SG 2 SG PLC setpoint SG 2.4

29 Conclusion 28 Although h a Jig plant have a simple process, controlling a Jig plant to perform efficient is not that simple A lot of the setting and parameters of the Jig is interlinked which makes it difficult to control The more you work with a jig the better you will understand the interaction between the settings There is a place for Coal Jig operations in South Africa

30 29 Thank you Comments & Questions? Mauritz Lundt